Biomedical subjects
Publications and source records attributed to Israel Goldberg.
Crystals of the title compound, [Zn(C45H28N4O2)(H2O)].2C6H5NO2, consist of multiporphyrin supramolecular assemblies sustained by intermolecular COOH...COOH and Zn(H2O)...COOH hydrogen bonds. One of the two nitrobenzene solvent molecules hydrogen bonds peripherally to these arrays.
Chiral Salan ligands were found to wrap in a highly diastereoselective manner around zirconium leading to C2-symmetric complexes of predetermined chirality at the metal. These complexes led to active polymerization of higher olefins, their activity and isospecific induction depending on the nature of the phenolate substituents.
The crystal structure of the title compound, {[Zn(C52H36N4O8)].2C4H9NO}n, consists of two-dimensional coordination polymers of the six-coordinate zinc-porphyrin unit [Zn-N = 2.039 (2) and 2.061 (2) A, and Zn-O = 2.540 (2) A], which intercalate between the molecules of N,N-dimethylacetamide solvent. The Zn atom lies on an inversion centre.
The crystal structure of the title compound, [Zn(C46H24N8)(CH4O)], consists of two-dimensional supramolecular arrays sustained by O-H...N(pyridyl) hydrogen bonding and weak Zn...NC coordination. The interlayer organization in the crystal structure is characterized by tight stacking of the corrugated layers.
Upon the addition of Br2 to complexes (P-P)Pt(Ar)2, two different products were observed, depending on the bite angle of the bidentate phosphine ligand: a Pt(II) aryl bromide complex, the product of C-Br reductive elimination, and Pt(IV) oxidative addition complex. At high temperatures, the latter exclusively gave the product of the C-C reductive elimination.
Reaction between the 1,3-bis(trimethylsilyl) ether of calix[4]arene and platinum(II) difluoro complexes unexpectedly results in the formation of the 1,2-bridging platinum(II) calixarene complex, which, upon treatment with 2 equiv of acyl chloride, reinstates the 1,3-disubstitution pattern in the calixarene moiety.
The synthesis of alkoxotitanium(IV) and -zirconium(IV) complexes of seven chelating tetradentate di- or trianionic amine-phenolate ligands belonging to three families and their application in L-lactide polymerization are described. The isopropoxotitanium complexes were synthesized by a direct reaction between the ligand precursors and titanium tetraisopropoxide, whereas the zirconium complexes were synthesized by various routes. For titanium, complexes of all seven ligands could be synthesized. For zirconium, the hexacoordinate complexes derived from all dianionic ligands were synthesized; however, the only pentacoordinate complex that could be produced was the one derived from the bulky trianionic ligand. X-ray structures of zirconium complexes of the three families indicated a substantial pi donation from the alkoxo ligand to the metal. All complexes were found to be active lactide polymerization catalysts, and their activity was found to depend strongly on the metal, the coordination number around the metal, and the phenolate substituents but not on the ligand backbone.
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Two molybdenum and three antimony corroles were isolated and characterized by NMR, EPR, and electrochemistry. The very negative reduction potentials of the (oxo)molybdenum(V) corroles are clearly related to their inactivity as oxygen transfer reagents and the unsuccessful attempts to isolate lower-valent molybdenum corroles. X-ray crystallography of the (oxo)molybdenum(V) corrole 1a and the trans-difluoroantimony(V) corrole 2c, the first of their kind, revealed that their molecular structures represent extreme cases of such complexes: a highly domed corrole with very large out-of-plane metal displacement for 1a (0.73 Angstroms) and a very flat corrole with the metal ion in its center for 2c. All three antimony corroles displayed high activity and selectivity as catalysts for the photoinduced oxidation of thioanisole by molecular oxygen, with superior results obtained in alcoholic solvents with 2c as catalyst. Allylic and tertiary benzylic CH bonds were also oxidized under those conditions, with absolute selectivity to the corresponding hydroperoxides.
The title compound, bis[(-)-N-(trans-4-isopropylcyclohexanecarbonyl)-D-phenylalanine] hydronium chloride, 2C19H27NO3.H3O+.Cl-, at 110 K contains four conformationally dissimilar moieties in the asymmetric unit, which are seemingly necessary in order to optimize the supramolecular association. The organic molecule forms O-H...O hydrogen-bonded carboxylic acid dimers, which are paired into six-component clusters via N-H...Cl hydrogen bonds through the two bridging chloride anions. These combined hexameric aggregates are further interlinked into extended two-dimensional network arrays via the hydronium ions by O-H...O and O-H...Cl hydrogen bonds. This study represents the first crystallographic report of nateglinide.
Fexofenadine [systematic name: (+/-)-(4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)piperidinium-1-yl]-butyl]phenyl)-2-methylpropionate], crystallizes in two forms, viz. as the methanol disolvate, C32H39NO4.2CH4O, and as the dihydrate, C32H39NO4.2H2O. It exists in the two structures as a zwitterion, which self-assembles as dimers sustained by a pair of charged-assisted N-H...OOC hydrogen bonds. In the methanol disolvate, the supramolecular organization consists of discrete fexofenadine dimers solvated by four molecules of methanol. The dihydrate structure is sustained by a more extended hydrogen-bonding scheme, wherein the hydrated dimeric entities are interlinked by additional hydrogen bonds. The fexofenadine molecule adopts different and differently disordered conformations of the 1-hydroxybutyl residue in the two structures.
An amine mono(phenolate) ligand bearing two side-arm donors led to octahedral trialkoxo and trialkyl group IV metal complexes, in which one of the donors was unbound, and to exceptionally stable cationic complexes in which the two side-arm donors were tightly bound.
The coordination chemistry of amine tris(phenolate) ligands around V(III) and V(V) is described for the first time. Three amine tris(phenolate) ligands were employed featuring different steric and electronic influence exerted by the phenolate substituents in the ortho and para positions being either t-Bu, Me, or Cl. V(III) complexes of all ligands (1-3) were readily obtained by reaction between the ligand precursors and VCl3(THF)3 in the presence of triethylamine. The complexes obtained were pentacoordinate, a THF ligand completing the coordination sphere of the metal, which was found to be of almost perfect TBP geometry, as revealed by crystallography. V(V) oxo complexes of all the ligands (4-6) were readily obtained by a reaction between the ligand precursors and VO(OPr)3. The oxo complexes of the alkyl-bearing ligands (4 and 5) could also be synthesized by the air oxidation of the corresponding V(III) complexes (1 and 2); however, the attempted air oxidation of the V(III) complex bound to the electron-poor ligand (3) did not yield the corresponding oxo complex 6. 1H NMR and crystallographic analysis of complexes 4 and 5 supported their TBP structures. Complex 6, on the other hand, was found to be composed of a TBP complex (6a) and an octahedral complex (6b) in equilibrium, the octahedral complex being more stable at lower temperatures. An X-ray structure of 6b revealed a mononuclear oxo complex, the sixth coordination site being occupied by an aqua ligand to which two THF molecules are H-bonded. Complexes 4-6 catalyze the epoxidation of olefins by t-BuOOH, albeit slowly. These complexes may thus be considered as structural and functional models of vanadium-dependent haloperoxidase enzymes.
The degree of diastereoselectivity in the wrapping of four new chiral Salan ligands to form chiral-at-metal titanium complexes ranged from mild to perfect as a function of the ligands' N substituents; the enantiomerically pure complexes catalyzed the addition of diethyl zinc to benzaldehyde in 73-76% enantiomeric excess.
This work describes the synthesis and characterization of mononuclear and dinuclear Ru(II) and Os(II) complexes based on the symmetrical bridging ligand isoeilatin (1). The crystal structure of 1.[HCl]2 consists of layers of tightly pi-stacked molecules of the biprotonated isoeilatin. The mononuclear complexes [Ru(bpy)2(ieil)]2+ (2(2+)) and [Os(bpy)2(ieil)]2+ (3(2+)) form discrete dimers in solution held together by face-selective pi-stacking interactions via the isoeilatin ligand. Coordination of a second metal fragment does not hinder the pi-stacking completely, as demonstrated by the concentration dependence of the 1H NMR spectra of the dinuclear complexes [{Ru(bpy)2}2{mu-ieil}]4+ (4(4+)), [{Os(bpy)2}2{mu-ieil}]4+ (5(4+)), and [{Ru(bpy)2}{mu-ieil}{Os(bpy)2}]4+ (6(4+)) and supported by the solid-state structure of meso-4.[Cl]4. The bridging isoeilatin ligand conserves its planarity even upon coordination of a second metal fragment, as demonstrated in the solid-state structures of meso-4.[Cl]4, meso-4.[PF6]4, and meso-5.[PF6]4. All of the dinuclear complexes exhibit a preference (3/2-3/1) for the formation of the heterochiral as opposed to the homochiral diastereoisomer. Absorption spectra of the mononuclear complexes feature a low-lying dpi(M) --> pi*iel MLCT band around 600 nm that shifts to beyond 700 nm upon coordination of a second metal fragment. Cyclic and square-wave voltammetry measurements of the complexes exhibit two isoeilatin-based reduction waves that are substantially anodically shifted compared to [M(bpy)3]2+ (M = Ru, Os). Luminescence spectra, quantum yields, and lifetime measurements at room temperature and at 77 K demonstrate that the complexes exhibit 3MLCT emission that occurs in the IR region between 950 and 1300 nm. Both the electrochemical and photophysical data are consistent with the low-lying pi orbital of the isoeilatin ligand. The dinuclear complexes exhibit two reversible, well-resolved, metal-centered oxidation waves, despite the chemical equivalence of the two metal centers, indicating a significant metal-metal interaction mediated by the bridging isoeilatin ligand.
In the title compound, diaquabis(1,4-di-4-pyridyl-2,3-diaza-1,3-butadiene)dimethanolzinc(II) bis(perchlorate) 1,4-di-4-pyridyl-2,3-diaza-1,3-butadiene methanol 1.72-solvate 1.28-hydrate, [Zn(C12H10N4)2(CH4O)2(H2O)2](ClO4)2.C12H10N4.1.72CH4O.1.28H2O, determined at ca 110 K, the Zn cation and the extended dipyridyl ligand both lie across inversion centres in space group P-1. The structure consists of a network arrangement of the constituent species stabilized by a combination of coordination, hydrogen bonding and pi-pi forces. Uncoordinated methanol and water solvent molecules occupy the otherwise void spaces within and between the networks.
Complexes (R3P)2PtF2 were prepared by reaction of the corresponding diiodo precursors with AgF in dichloromethane. The intermediate formation of trans- and cis-(R3P)2Pt(I)F was also observed. All fluoro complexes demonstrate a strong preference for the cis-configuration (R = Ph or Et) unless a bulky phosphine ligand is used (R = i-Pr), in which case the trans complex was observed. The Pt(IV) difluoro compounds (R3P)2Ar2PtF2 were obtained by reacting the Pt(II) diaryl precursors with XeF2. The fluoro ligands are located in the trans-position relative to the aryl groups in the overall octahedral environment. The representative Pt(II) and Pt(IV) difluoro complexes were characterized by X-ray crystallography. All fluoro compounds react rapidly with chlorotrimethylsilane to give the corresponding chloro complexes. The Pt(IV) difluorides are remarkably stable in the C-C reductive elimination reaction, relative to their dichloro analogs which reductively eliminate diaryl within several hours at 45 degrees C in N-methylpyrrolidone. It was found that phosphine dissociation from the octahedral Pt(IV) complex is essential for the reductive elimination reaction to take place, the difluoro complex being kinetically stable even at 60 degrees C.
This article describes recent achievements made by us and other groups in targeted synthesis of porphyrin-based framework solids by various non-covalent mechanisms of molecular recognition. The self-assembly processes are effected in a tunable manner either by direct association of suitably designed porphyrin building blocks, or by their supramolecular aggregation through external linkers as metal ions and organic bi-dentate ligands. Many of these crystalline porphyrin materials exhibit open architectures and remarkable structural integrity, and their potential application for selective guest storage and molecular sieving is highlighted.